Certain measures have to be taken in order to provide for adequate shielding of gamma and neutron radiation for containers holding radioactive materials. For the purposes of additionally shielding the neutron radiation which comes from the radioactive nuclear fuel, the usual practice is to provide a neutron shielding layer of a hydrogen-bearing material, preferably polyethylene, around the storage container. Because of the poor thermal conductivity of such neutron-shielding materials, it is known to arrange thermally-conductive struts in that layer to connect the surface of the container with the outside atmosphere.
German published patent application DE-OS No. 28 31 646 discloses a shielding container which has a neutron-shielding layer of granular polyethylene and in which the heat-conducting struts are connected to an external surface of a relatively thin-walled steel jacket to provide for better discharge of the decay heat to the ambient. The thin steel jacket serves only to provide for a good discharge of the decay heat to the ambient.
In the case of double container systems in which the containers are disposed one within the other and must fulfill different requirements, the shielding container has a wall thickness which is usually 200 mm in order to provide the necessary shielding against radioactive radiation. In addition, the thick-walled outer shielding container is to provide mechanical protection for the inner container during transport and when subjected to impact loadings. The inner storage container accommodates the radioactive materials in a gas-tight manner. For this purpose, the inner storage container is provided with a double cover system. The outer secondary cover is welded to the body of the container in a gas-tight manner.